Western Bean Cutworm

Striacosta albicosta

Western bean cutworm larva
Western bean cutworm larva. Photo courtesy of Adam Sisson, Iowa State University. Licensed under CC BY 3.0.
Western bean cutworms were initially a problem in Iowa but have since spread throughout the corn belt. They are a late season pest of primarily corn although they also attack dry beans.
Brown moths with a wingspan of 1.5". The forewings have a white leading edge and a distinct crescent marking.
Western bean cutworm moth
Western bean cutworm adult. Photo courtesy of Adam Sisson, Iowa State University. Licensed under CC BY 3.0.
Larva grow to a length of 1.5". Young larva are dark colored and have a diamond shaped pattern on their back. More mature larva are lighter in color and have three distinct lines behind the head. The larva lack lateral lines on their body, distinguishing them from other corn pests such as corn earworm and fall armyworm.
Western bean cutworm larva
Western bean cutworm larva. Photo courtesy of Frank Peairs, Colorado State University. Licensed under CC BY 3.0.
Each egg mass typically contains around 50 eggs, and progresses in color from white to dark purple.
Western bean cutworm egg mass
Western bean cutworm egg mass. Photo courtesy of Frank Peairs, Colorado State University. Licensed under CC BY 3.0.
Unlike most cutworms, western bean cutworms are a late season pest of corn. They are particularly distructive because they directly attack the ear. This damage is often followed by secondary mold infections, resulting in potentially high yield loss.
Several insecticies are available for controlling western bean cutworm. For maximum effectiveness, they need to be applied when the larva are small since mature larva tend to burrow into the plant and are then protected from pesticides. Always read and follow all label instructions.
Bt corn hybrids with the Cry1F trait provide protection against western bean cutworm.